Method of sealing a porous fibrous substrate, and door skins, produced by the method

ABSTRACT

A method of surface sealing a porous fibrous substrate is provided. According to the method, a porous fibrous substrate possessing a moisture content and a surface with pores is provided. A sealant composition is applied to a surface of the porous fibrous substrate and permitted to penetrate the surface pores of the porous fibrous substrate and undergo cure while participating in a foaming reaction with the moisture content to establish a water-resistant polymeric foam sealant impregnated into the porous fibrous substrate. The water-resistant polymeric foam sealant contains a polyurethane and/or polyurea.

FIELD OF THE INVENTION

The present invention relates to a method of making consolidatedcellulosic door skins and other articles having a sealer coat, and to amethod of making a door having a door skin with a sealer coat. Thepresent invention also relates to door skins, doors, and other articlesmade by the method.

BACKGROUND OF THE INVENTION

Man-made consolidated cellulosic articles, such as fiberboard, may bemolded to have either planar or three-dimensional shapes and embossedwith various designs and patterns, such as a wood grain appearance ofnatural wood. Fiberboards are a well known and widely used class ofconsolidated cellulosic articles that include such materials ashardboard, soft board, and medium-density fiberboard (MDF). Chipboardssuch as particleboard, medium-density particleboard, and orientedstrandboard (OSB) constitute another useful class of consolidatedcellulosic articles. Composite structures of these boards are alsouseful.

Various processes have been practiced to produce consolidated compositearticles such as those mentioned above. The principal processes for themanufacture of consolidated composite articles include wet felted/wetpressed or “wet” processes; dry felted/dry pressed or “dry” processes;and wet felted/dry pressed or “wet-dry” processes.

Generally, in a wet process, cellulosic materials such as fibers (e.g.,fibrillized wood fibers) are blended in a vessel with large amounts ofwater to form a slurry. The slurry preferably has sufficient watercontent to suspend a majority of the cellulosic fibers and preferablyhas a water content of at least ninety weight percent of the woodfibers. (All percentages disclosed herein are by weight, unlessspecifically stated otherwise.) The slurry is combined with a syntheticresin binder, such as for example a phenol-formaldehyde resin, anddeposited onto a water-pervious support member, such as a fine screen,where much of the water is removed to leave a wet mat. The resultingcellulosic material has a moisture content, for example, of about fiftyweight percent based on the dry weight of the cellulosic material. Thewet mat is transferred from the pervious support member to a press andconsolidated under heat and pressure to form the consolidated compositearticle, such as a door facing or other desired article.

A wet-dry forming process typically includes blending cellulosic rawmaterial, e.g., wood fibers, in a vessel with large amounts of waterhaving a pH of less than seven to form a slurry. This slurry is thenblended with a resin binder. As in the wet process described above, theblend is then deposited onto a water-pervious support member, where alarge percentage of the water is removed, thereby leaving a wet mat ofcellulosic material having a water content of about fifty weightpercent, for example. This wet mat is then transferred to an evaporationzone where much of the remaining water is removed by evaporation. Thedried mat preferably has a moisture content of less than about thirtyweight percent based on the dry weight of the cellulosic material. Thedried mat is then transferred to a press and consolidated under heat andpressure to form the consolidated composite article.

In a dry process, the cellulosic material is generally conveyed in agaseous stream or by mechanical means rather than a liquid stream. Thecellulosic material may be first coated with a thermosetting resinbinder, such as a phenol-formaldehyde resin. The cellulosic material isthen randomly formed into a mat by air blowing one or more layers of theresin-coated cellulosic material onto a support member. The mat mayoptionally be subjected to pre-press drying. The mat, typically having amoisture content of less than about thirty weight percent and preferablyless than about ten weight percent, is then pressed under heat andpressure to cure the thermosetting resin and to compress the mat into anintegral consolidated article.

In the processes described above, the mat is typically consolidated in apress between upper and lower press platens. After compression, theresulting molded article may include a surface intended to be exteriorlydisposed, such as a door facing exterior surface. The aestheticappearance and physical properties of the exterior surface may playimportant roles in evaluating the quality and functionality of thearticle. However, the compression process sometimes results in anarticle having a surface with undesirable qualities. For example, thesurface of the article removed from the press may possess imperfectionssuch as cracks, voids and high porosity. Without wishing to benecessarily bound by any theory, it is believed that these defects aregenerated when the consolidated material “sticks” to the platens as theplatens release. These imperfections not only adversely affect theaesthetic quality of the door skin, but also deleteriously affectimportant properties, such as reducing surface hardness. Even ifsufficient press release is achieved, the surface quality of the articlemay still be inadequate, given the high surface porosity often presentin a consolidated cellulosic article.

In order to provide the desired surface characteristics to the finishedproduct, a sealer or finish coat may be applied to the molded articleafter removal of the molded consolidated composite article from thepress. Often, the surface color is also desirably altered by theprecursory step of applying a primer to the surface of the moldedarticle, thereby providing a ready-to-finish surface on the compositearticles conditioned to accept paint or stain, for example. However,conventional sealers do not adequately fill the relatively large surfacecracks, voids, and pores sometimes present in consolidated cellulosicarticles. As a result, the consolidate cellulosic articles, even afterreceipt of a surface treatment, may possess a poor surface seal and highwater sensitivity and permit moisture penetration. Articles such asexterior door facings are often exposed to large amounts of water (e.g.,rain and high humidity). The penetration of moisture into a poorlysealed surface of a consolidated cellulosic article can lead to fiberswelling, which can manifest as cosmetic blemishes and blistering,making the article commercially unacceptable to discriminatingconsumers.

SUMMARY OF THE INVENTION

In accordance with the purposes of the invention as embodied and broadlydescribed herein, according to a first aspect of this invention there isprovided a method of surface sealing a porous fibrous substratepossessing a moisture content and a surface with pores. The methodfeatures applying a sealant composition to the surface of the porousfibrous substrate and permitting the sealant composition to penetratethe surface pores of the porous fibrous substrate. The sealantcomposition undergoes cure while participating in a foaming reactionwith the moisture content to establish a water-resistant polymeric foamsealant impregnated into the porous fibrous substrate. Thewater-resistant polymeric foam sealant comprises a polyurethane and/or apolyurea.

According to a second aspect of the invention, a sealed article isprovided. The sealed article features a porous fibrous substratepossessing surface pores, and a water-resistant polymeric foam sealantselected from a polyurethane and polyurea impregnated in the surfacepores of the porous fibrous substrate to establish a water-resistantfoam seal.

According to a third aspect of the invention, a method is provided formaking a door. The method comprises providing a first door skincomprising a porous fibrous substrate possessing surface pores and amoisture content and having a first interior surface and a firstexterior surface. A sealant composition is applied to the first exteriorsurface, and is permitted to penetrate the surface pores of the porousfibrous substrate and undergo cure while participating in a foamingreaction with the moisture content to establish a water-resistantpolymeric foam sealant impregnated into the porous fibrous substrate.The polymeric foam sealant is selected from a polyurethane and polyurea.The first interior surface is attached to a first side of a door frame.A second door facing having a second interior surface and a secondexterior surface is provided, and the second interior surface of thesecond door facing is attached to a second side of the door frame.

A fourth aspect of the invention provides a door comprising a door framehaving opposite first and second sides, a first door facing having afirst interior surface attached to the door frame and a first exteriorsurface facing away from the door frame, and a second door facing havinga second interior surface attached to the door frame and a secondexterior surface facing away from the door frame. At least one of thedoor facings comprises a sealed article featuring a porous fibroussubstrate possessing surface pores, and a water-resistant polymeric foamsealant selected from a polyurethane and polyurea impregnated in thesurface pores of the porous fibrous substrate to establish awater-resistant foam seal.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are incorporated in and constitute a part ofthe specification. The drawings, together with the general descriptiongiven above and the detailed description of the preferred embodimentsand methods given below, serve to explain the principles of theinvention. In such drawings:

FIG. 1 is a flow diagram of a method according to an embodiment of theinvention;

FIG. 2 is a partial cross-sectional view of an apparatus for making aconsolidated cellulosic article, depicting the apparatus in apre-compression state;

FIG. 3 is a partially cross-sectional view of the apparatus of FIG. 2,depicting the apparatus in a post-compression state;

FIG. 4 is an elevated perspective view of an embodiment of a six-paneldoor in accordance with the invention; and

FIG. 5 is a cross-sectional view taken along line V-V of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS AND PREFERRED METHODS OFTHE INVENTION

Reference will now be made in detail to preferred embodiments andmethods of the invention as illustrated in the accompanying drawings, inwhich like reference characters designate like or corresponding partsthroughout the drawings. It should be noted, however, that the inventionin its broader aspects is not limited to the specific details,representative devices and methods, and illustrative examples shown anddescribed in this section in connection with the preferred embodimentsand methods.

Referring more particularly to the illustrated embodiments, FIG. 1depicts a process according to an embodiment of the invention. At step10, a porous fibrous substrate possessing surface pores and a moisturecontent is provided. The porous fibrous substrate is preferably aconsolidated cellulosic article, such as a medium density fiberboardparticle board, plywood, fiberboard, pegboard, cloth or fabric.Preferably, the cellulosic article contains wood fibers and/orparticles.

The porous, fibrous substrate may be manufactured elsewhere ormanufactured on site. Suitable manufacturing techniques include the wetprocesses, dry processes, and wet-dry processes described above.Referring now to FIGS. 2 and 3, an apparatus for forming consolidatedcellulosic articles is generally depicted by reference numeral 20. A mat22 of uncompressed cellulosic material is shown disposed between a firstdie 23 mounted to a first platen 24, and a second die 25 mounted to asecond platen 26.

The facing surfaces of dies 23, 25 may be contoured to emboss desiredshapes and/or patterns, e.g., panels, in mat 22. First die 23 includes asubstantially flat top 31, sides 32 and 34, as well as a base 36. Seconddie 25 includes a bottom 38, sides 40 and 42, and a top 44. Second die25 includes a plurality of forms 46 extending from bottom 38. Forms 46are uniformly spaced apart by a plurality of voids 48. In the depictedembodiment, the forms 46 are bulbous or frusto-conical, having angled,arcuate, or canted sides 47. The angled sides 47 may be at a range ofdegrees, for example, from about 5 degrees to about 45 degree fromvertical. It should be understood that top 31 of first die 23 maypossess an identical, complementary, or alternative shape to that of thefacing surface of second die 25. Similarly, bottom 38 of second die 25may be flat. Additionally, the facing die surfaces also may containtapered sides and other designs, or example, as described in U.S. Pat.No. 6,972,150.

First and second dies 23 and 25 may be manufactured from a suitably hardmaterial such as steel or aluminum, and are mounted to platens 24, 26,respectively, for relative movement toward each other. In the depictedembodiment, the mechanism for moving first and second platens 24 and 26toward one another is provided in the form of a cylinder 28 attached tosecond platen 26, which is preferably hydraulic, but which can beprovided in other forms, including pneumatic, as well as various formsof linear actuators. First platen 24 is fixed, but a similar cylinder orcylinders may be attached to first platen 24 as well. Each cylinder 28may be sized to produce a range of pressure outputs, such as in a rangeof about 3,000 psi to about 5,000 psi. The pressure exerted on mat 22may be, for example, in a range of about 400 psi to about 1000 psi.

A heat generation mechanism 29 is preferably provided such that mat 22is compressed under elevated temperatures as well. Heat generationmechanism 29 can take many forms including a source of heated oil orsteam circulated through conduits 30 in first and second platens 24, 26and first and second dies 23, 25. The achieved temperature is typicallyin a range of about 300° F. to about 500° F. (about 149° C. to about260° C.), depending on the curing temperature required by the particularbinding agent or resin being used.

Mat 22 may be comprised of any number of cellulosic materials andbinding agents to result in, when compressed under heat and pressure, aconsolidated cellulosic article 51 (FIG. 3). The cellulosic materialswithin mat 22 may include, but not be limited to, waste materials fromlumber mill operations such as sawdust, shavings, and wood chips, or maybe provided in the form of specially ground fibers of a specific size orrange of sizes. Thus, where fibers are referred to herein, it isunderstood that other materials could be substituted. The binding agentmay be in the form of various adhesives or resins including phenolformaldehyde, urea formaldehyde, melamine modified urea formaldehyde orisocyanic resins. Various materials and methods of manufacturingconsolidated cellulosic materials are described in U.S. Pat. Nos.5,306,539; 5,344,484; 5,367,040; 5,425,976; 5,470,631; 5,489,460;5,647,934; 5,756,599; and 5,847,058.

FIGS. 2 and 3 show a typical sequence of steps resulting in theformation of the board 51. Mat 22 is provided on first die 23, withsecond die 25 being spaced away due to cylinder 28 being retracted. Mat22 is typically provided in a semi-solid state after initial passagethrough, for example, pre-press rollers (not shown). The semisolid mat22 is then conveyed into position between first and second dies 23, 25.When cylinder 28 extends, second platen 26 moves toward mat 22, andcompresses mat 22 against first die 23. Cylinder 28, second platen 26,and second die 25 are then retracted away from first die 23 and platen24, and consolidated cellulosic board 51 is removed.

Consolidated cellulosic board 51 will have opposite surfaces matchingthe surface shapes and contours of first and second dies 23, 25. Forexample, in the illustrated embodiment forms 46 pressed against mat 22establish corresponding indented portions in compressed cellulosic board51. The indented portions are separated by raised portions correspondingto voids 48.

Consolidated cellulosic board 51 may comprise, for example, a fiberboardarticle (e.g., hardboard or medium density fiberboard (MDF)) or achipboard article (e.g., particleboard, medium-density particleboard, ororiented strand board (OSB)). Examples of consolidated cellulosic boardproducts include siding, door facings, pegboard, etc. The door facingsor skins may be useful for interior and exterior passageway and hallway,as well as for furniture, cabinet and closet doors, and drawers.

Consolidated cellulosic board 51 obtained from the above manufacturingprocesses will possess pores, voids, and/or cracks. Mean pore size mayrange, for example, from about 1 micron to about 300 microns, such asfrom about 20 microns to about 75 microns. Consolidated cellulosic board51 is preferably characterized by a moisture content sufficient to foamthe sealant composition, but preferably less than about 10 weightpercent.

In step 12 of FIG. 1, a sealant composition is applied to at least onesurface of consolidated cellulosic board 51. The sealant compositionpreferably comprises a polyurethane and/or polyurea precursor. Anexemplary composition is a two-part urethane composition with a polyolfirst part and a polyisocyanate second part. Examples of suitablepolyols include diols and triols, and may be selected from phenolics,polyethers and polyesters. The polyisocyanate may possess two or moreisocyanate functional groups, such as MDI (methylene diphenyldiisocyanate), NDI (naphthalene diisocyanate), TDI (toluenediisocyanate), and HDI (hexamethylene diisocyanate). Another exemplarycomposition is a two-part polyurea composition with a polyamine firstpart and a polyisocyanate second part. It is within the scope of theinvention to employ various compositions for forming the polyurethaneand/or polyurea, including compositions containing monomers, oligomers,and/or prepolymers.

The sealant composition may contain additional ingredients, such aschain extenders, blowing agents, flame retardants, and/or fillers.

The preferred application technique is spraying. For example, in thecase of a two-part urethane composition, a dual feed spray apparatuswith a static mixer at the head of the application gun may be used.Other suitable techniques for applying the sealant composition includedipping, brushing, and rolling. Generally, it is preferred to apply thesealant composition at substantially room temperature without preheatingof consolidated cellulosic board 51 or sealant composition. It ispreferred that the sealant composition be applied in an amount of about3 grams/ft² to about 4.5 grams/ft² (grams of composition per square footof porous fibrous substrate), although amounts outside this range arepossible. The temperature conditions may be varied, however, dependingupon such factors as the reactivity of the sealant composition.

In step 14, the sealant composition is permitted to penetrate thesurface pores of consolidated cellulosic board 51 and undergo cure whileparticipating in a foaming reaction with the moisture content of board51. The cured composition establishes a water-resistant polyurethaneand/or polyurea foam sealant impregnated into the pores of consolidatedcellulosic board 51. The extent of penetration will be dependent uponseveral factors, including the pore size of consolidated cellulosicboard 51 and the properties, e.g., viscosity, of the sealantcomposition. It is preferred that the sealant composition penetrateabout 50 microns to about 75 microns below the surface of board 51.

In step 16, board 51 may be subjected to further processing, such asmilling, shaping, painting, protective coating, hardware (e.g.,doorknob, hinges, knocker) attachment, assemblage (e.g., into a door),etc.

FIGS. 4 and 5 illustrate a door, generally designated 60, made accordingto an embodiment of the invention. Door 60 includes a front door facing(door skin) 62 and an identical, rear door facing (door skin) 64,secured to opposite major surfaces of a door frame or interior supportstructure 66. Typically, parallel side members, known as stiles,establish opposite sides of door frame 66, and parallel end members,known as rails, establish the top and bottom of door frame 66. The framemembers can be made of natural wood, man-made pressed wood, or any othersuitable material. Door facings 62, 64 are preferably molded so as toimpart aesthetic surface contours, such as wood grain patterning and/orpanel structures, in the visible exterior surfaces that correspond toessentially identical contours of a mold cavity, e.g., dies 23, 25. Theinterior surfaces of door facings 62, 64 are preferably secured, e.g.,with an adhesive, to a core component positioned within frame 66.

Door facings 62, 64 shown in FIGS. 4 and 5 are molded to simulatemulti-panel door surfaces. The embodiment shown in FIGS. 4 and 5contains two molded contoured regions 68, 70 that define and surroundtwo panels 72, 74, respectively. Panels 72, 74 are preferably coplanar.Each of the contoured regions 68, 70 is completely surrounded by asubstantially planar (e.g., horizontal) main surface portion 76.Optionally, panels 72, 74 lie in the same plane as main surface portion76.

The exterior surfaces of door facings 62, 64 are sealed according to theinvention, and may further be primed, painted, stained, and/or receiveother layers and/or protective coatings. Optionally, wood veneers may bebonded to the exterior surfaces to provide the surfaces with theappearance (e.g., color, grain and/or inlay patterns) of natural wood.Alternatively, an image can be printed on the exterior surfaces of doorfacings 62, 64, as described in U.S. Pat. No. 7,001,016.

Door 60 is hollow in the middle or is provided with a core. The core, ifpresent, may comprise a foam formed of any suitable polymer materialwhich can be injected and formed in place or can be pre-formed and thenplaced between door facings 62, 64 and surrounded by frame 66. Otherfoam materials include, for example, corrugated pads and otherinsulation and materials. It should be noted that door facings 62, 64may be adhered to the solid core, if present.

The foregoing detailed description of the certain preferred embodimentsof the invention has been provided for the purpose of explaining theprinciples of the invention and its practical application, therebyenabling others skilled in the art to understand the invention forvarious embodiments and with various modifications as are suited to theparticular use contemplated. This description is not intended to beexhaustive or to limit the invention to the precise embodimentsdisclosed. Modifications and equivalents will be apparent topractitioners skilled in this art and are encompassed within the spiritand scope of the appended claims and their appropriate equivalents.

1. A method of surface sealing a porous fibrous substrate, comprising:providing a porous fibrous substrate possessing a moisture content and asurface with pores; and applying a sealant composition to a surface ofthe porous fibrous substrate and permitting the sealant composition topenetrate the surface pores of the porous fibrous substrate and undergocure while participating in a foaming reaction with the moisture contentto establish a water-resistant polymeric foam sealant impregnated intothe porous fibrous substrate, the water-resistant polymeric foam sealantcomprising a member selected from the group consisting of a polyurethaneand polyurea.
 2. The method of claim 1, wherein the sealant compositioncomprises a two-part polyurethane composition comprising a first partcontaining a polyol, and a second part containing a polyisocyanate. 3.The method of claim 1, wherein the sealant composition comprises atwo-part polyurea composition comprising a first part containing apolyamine, and a second part containing a polyisocyanate.
 4. The methodof claim 1, wherein said applying comprises spraying the sealantcomposition on the porous fibrous substrate.
 5. The method of claim 1,wherein said applying establishes about 3 grams/ft² to about 4.5grams/ft² of the polymeric foam sealant per square foot of porousfibrous substrate.
 6. The method of claim 1, wherein the porous fibroussubstrate possesses a mean porosity size of about 1 micron to about 300microns.
 7. The method of claim 1, wherein the porous fibrous substratecomprises a cellulosic fiber and phenolic resin.
 8. The method of claim1, wherein the sealant composition penetrates about 50 to about 75microns below the surface of the porous fibrous substrate.
 9. The methodof claim 1, wherein the porous fibrous substrate comprises a door skin.10. The method of claim 9, wherein the door skin is embossed with a woodgrain pattern and comprises at least one panel region.
 11. A sealedarticle, comprising: a porous fibrous substrate possessing surfacepores; and a water-resistant polymeric foam sealant comprising a memberselected from the group consisting of a polyurethane and polyureaimpregnated in the surface pores of the porous fibrous substrate.
 12. Amethod of making a door, comprising: providing a porous fibrous firstdoor skin possessing a moisture content and having a first exteriorsurface with pores and a first interior surface; applying a sealantcomposition to the first exterior surface of the porous fibrous firstdoor skin and permitting the sealant composition to penetrate thesurface pores of the porous fibrous first door skin and undergo curewhile participating in a foaming reaction with the moisture content toestablish a water-resistant polymeric foam sealant impregnated into theporous fibrous first door skin, the water-resistant polymeric foamsealant comprising a member selected from the group consisting of apolyurethane and polyurea; attaching the first interior surface to afirst side of a door frame; providing a second door skin having a secondinterior surface and a second exterior surface; and attaching the secondinterior surface of the second door skin to a second side of the doorframe.
 13. The method of claim 12, wherein the sealant compositioncomprises a two-part polyurethane composition comprising a first partcontaining a polyol, and a second part containing a polyisocyanate. 14.The method of claim 12, wherein the sealant composition comprises atwo-part polyurea composition comprising a first part containing apolyamine, and a second part containing a polyisocyanate.
 15. The methodof claim 12, wherein said applying comprises spraying the sealantcomposition on the first exterior surface of the porous fibrous firstdoor skin.
 16. The method of claim 12, wherein said applying establishesabout 3 grams/ft² to about 4.5 grams/ft² of the polymeric foam sealantper square foot of porous fibrous door skin.
 17. The method of claim 12,wherein the porous fibrous first door skin possesses a mean porositysize of about 1 micron to about 300 microns.
 18. The method of claim 12,wherein the porous fibrous first door skin comprises a cellulosic fiberand phenolic resin.
 19. The method of claim 12, wherein the sealantcomposition penetrates about 50 to about 75 microns below the firstexterior surface of the porous fibrous first door skin.
 20. A door,comprising: a door frame having a first frame side and an oppositesecond frame side; a first door skin comprising a porous fibroussubstrate having an exterior surface possessing surface pores and aninterior surface, the first door skin being attached to the first frameside; a water-resistant polymeric foam sealant comprising a memberselected from the group consisting of a polyurethane and polyureaimpregnated in the surface pores of the porous fibrous substrate; and asecond door skin attached to the second frame side.